1. Field of the Invention
The present invention relates to an electronic thermometer.
2. Description of the Related Art
Conventionally, there has been known an electronic thermometer having a buzzer for notifying user of temperature measurement end time or the like. For such an electronic thermometer, increasing of the sound volume in a small size buzzer is a technical problem.
As art for increasing the sound volume of such a small size buzzer, there have been known arts of forming a resonant space which resonates with vibration sound of a vibration plate provided on the buzzer, and providing a case or the like for supporting the buzzer with a sympathetic vibrating portion which vibrates sympathetically with vibration of the vibration plate (see Japanese Patent Application Laid-Open No. 2004-20241). To exert the resonance action and sympathetic vibration action effectively, it is indispensable to vibrate the vibration plate provided on the buzzer according to a setting. Then, to vibrate this vibration plate according to the setting, the buzzer (vibration plate) needs to be fixed accurately at a desired position. Therefore, in order to increase the sound volume in a small size buzzer, buzzer fixing structure is an important factor.
An example of the buzzer fixing structure in a conventional electronic thermometer will be described with reference to FIG. 12. FIG. 12 is a sectional view of an electronic thermometer of a conventional example. FIG. 12 shows a section of a portion perpendicular to the longitudinal direction of the electronic thermometer and provided with a buzzer.
In an electronic thermometer 200 of this conventional example, an inner case 220 having various major components is pressed into an outer case 211 constructing its appearance and having waterproof property. The inner case 220 is provided with a buzzer cover 270 and the buzzer 280 is positioned and fixed by this buzzer cover 270 and the inner case 220. The buzzer 280 has a piezoelectric plate which is provided integrally on a vibration plate. Then, the vibration plate of this buzzer 280 is fixed such that it is sandwiched from both face sides by a supporting portion 221 provided in the inner case 220 and a pair of pressing portions 273 provided on the buzzer cover 270 in the vicinity of an edge of the vibration plate.
The buzzer cover 270 is provided with a pair of projecting portion 272 which makes contact with the inner wall face of the outer case 211 with the inner case 220 mounted on the outer case 211. The pair of the projecting portion 272 makes contact with the inner wall face of the outer case 211 and the pair of the pressing portions 273 makes contact with the vibration plate of the buzzer 280, so that the buzzer cover 270 is fixed such that it is sandwiched form both face sides. As a consequence, the vibration plate of the buzzer 280 is positioned and fixed such that it is sandwiched from the both face sides by the buzzer cover 270 and the inner case 220.
When the buzzer 280 is positioned and fixed, resonant space R is formed in a region surrounded by the buzzer 280 and the inner case 220. Then, when the resonant space R resonates with vibration sound of the vibration plate of the buzzer 280 so that the inner case 220 vibrates sympathetically with vibration of the vibration plate 220, a large sound volume can be produced even if the buzzer 280 is small.
However, to generate the resonance action and sympathetic vibration action effectively, the vibration plate of the buzzer 280 needs to be fixed accurately at a desired position (a designed position). That is, the resonant space R is formed under a condition that the resonance action occurs when the vibration plate of the buzzer 280 is vibrated such that its central portion is vibrated most largely and the characteristic frequency of the inner case 220 is set so that the sympathetic vibration action occurs. Thus, unless the vibration plate of the buzzer 280 is fixed accurately at a desired position, a position vibrated most largely of the vibration plate is shifted from its central portion, so that the resonance action and sympathetic vibration action become insufficient.
To fix the vibration plate of the buzzer 280 accurately at a desired position, the dimensional accuracy of the outer case 211, the inner case 220, the buzzer cover 270, and the vibration plate of the buzzer 280 itself, and assembly accuracy of these members need to be intensified. The reason is that the positioning and fixing accuracy of the vibration plate of the buzzer 280 is almost determined by the dimension of an insertion hole (insertion hole in which the inner case 220 or the buzzer cover 270 is to be inserted) formed in the outer case 211, the height of the inner case 220 (distance from the bottom face of the inner case 220 up to the surface of the supporting portion 221 in FIG. 12), the thickness of the vibration plate portion of the buzzer 280, and the height (distance in the height direction from a front end of the projecting portion 272 to a front end of the pressing portion 273) of the buzzer cover 270.
Thus, if dimensional error between the left side portion and the right side portion of each member is large in a condition in which respective members are assembled in FIG. 12, an end portion of the buzzer 280 is nipped strongly so that the nipping of the other end portion is weakened. Therefore, when the vibration plate of the buzzer 280 is vibrated, the position vibrated most largely is shifted to the other end portion. Consequently, the resonance action and sympathetic vibration action become insufficient. The factor for accelerating the dimensional error includes a factor due to the dimensional accuracy of each of the members and a factor due to the assembly accuracy of each of the members.
In the structure shown in FIG. 12, the dimensional allowance of a distance in the height direction from the front end of the projecting portion 272 of the buzzer cover 270 to the front end of the pressing portion 273 needs to be 0.1 mm or less when the respective members are assembled.
As described above, in the conventional structure, the dimensional accuracy of each member and the assembly accuracy of each member need to be intensified although it is capable of generating a large sound volume with the small buzzer 280. For the reason, the dimensional accuracy of a mold for forming each member needs to be intensified and the dimensional control and assembly accuracy of each member needs to be made strict. This leads to increase of manufacturing cost.